Water Balance

Question 0

What adaptions were favored for land plants?

Answer 0

1. Preventing water loss, which kept cells drying out and dying.
2. Providing protection from harmful UV radiation
3. Moving water from tissues with direct access to water to tissues without direct access.

Question 1

What are the benefits of plants living on land?

Answer 1

1. Light: the water absorbs or reflects light. As a result, the amount of light available to drive for photosynthesis is reduced.
2. Carbon dioxide: most important molecule for photosynthesis - is more abundant in the atmosphere and diffuses more readily there than in water.

Question 2

What is the function of the cuticle?

Answer 2

Cuticle prevents water loss from the leaves

Reflects some UV light.

Question 3

What is the problem with the cuticle and it’s solution?

Answer 3

The cuticle also prevents intake of CO2, necessary for photosynthesis.

Solution are pores called stomata (sin. stoma)

Question 4

Function and structure of stoma

Answer 4

Function: allows gas exchange and allows for control of water loss
Structure: has “guard cells” that open and close the stomata

Found in all plants except liverworts - have pore but no guard cells

Question 5

How do guard cells work?

Answer 5

• To close the stomata, guard cells lose water and become flaccid.
• To open the stomata, guard cells take in water and become turgid, opening the pore.

Question 6

When are pores open and closed?

Answer 6

Pores are normally closed at night to limit water loss from the plant when CO2 is not needed.

Question 7

How do plants protect themselves from UV?

Answer 7

• cuticle reflects
• UV-absorbing compounds (eg. Flavonoids)

Protects DNA

Question 8

What are the two problems plants overcame to grow erect?

Answer 8

1. Transporting water from tissues that are in contact with wet soil to tissues in contact with dry air, against the force of gravity
2. Becoming rigid enough to avoid falling over in response to gravity and wind

Turns out both were solved by vascular tissue

Question 9

Defining feature of vascular tissue

Answer 9

Lignin

Question 10

Tracheids

Answer 10

Water conducting

Long, thin, tapering cells that have a thickened,

lignin-containing secondary cell wall in addition to a cellulose based primary cell wall

Question 11

Vessel elements

Answer 11

Most advanced type of water conducting cells

Are shorter and wider
Upper/lower ends have gaps where there is no cell wall
Reduce resistance and make water movement more efficient